Solving a DC Circuit with OpAmp

So I know that for a opamp, it does not draw any currents into its input side and the nodes b and c are the same potential. To figure out the potential at node b, i need to know I_6, but that 6k resistor is messing everything up.

If I assume that the 6k resistor is parallel to other 6k resistors then I can solve for I_6=1 mA
However, if that is the case then I_12=1 mA as well. But that means that the resulting voltage at node d is 0...which does not make sense..
Furthermore, from node c, I can use that to solve for the potential at node d.

I cannot say all three 6k resistors are in series since from that diagram it does not seem to be unless the ground has to do something with it.